Multiple user sessions are well known in the telephony field in the form of what are known as conference calls. In a conference call, all users are connected to a given location, often an advanced telephone of a call originator but alternatively a location belonging to the telephone service provider. The location receives all signals and mixes them for sending to each user. Mixing of the signals has a particular disadvantage in that specific hardware is needed, thereby increasing cost. Conference calls generally require specialized telephones in order to provide the support necessary for setup of such a conference call, and therefore, it is generally more difficult to arrange a conference call from a standard telephone. The specialized telephone may require support from office private branch exchange (PBX) hardware. If office PBX hardware is being used to set up the conference call, then it may be necessary for all participants to be called from the setup location in order to activate the conference call. In any of the above cases, there is often a limit on the number of participants to the conference call. As an alternative, the hardware needed for the conference call can be provided at the exchange. In such a case, an advanced telephone is not needed for call setup, but it may be necessary for each participant in the conference to call a central location. Usually in such circumstances, the conference call is arranged in advance and the users are notified of the time and the number to call.
Another kind of multi-party communication session is that provided by standard radio connections involving a base station and mobile units, such as commonly used by taxi companies, the police, and military for example. In these cases, a single channel is reserved for the group. Each member of the group is able to speak to each other member of the group via the base station. At any given time, only a single user is allowed to speak, and all the other users are limited to listening.
Numerous variations of the above radio system allow, for example, for dispensing with the base station in favor of one of the mobile units being set as master, or in favor of a circular connection system.
Disadvantages of the mobile radio system include limited range, although the range can be extended with the use of repeaters, and a closed group of users. The base station may be limited in capacity, and in any case, each user must be supplied with a mobile unit. These disadvantages do not apply to the conference call, in which anyone who is able to connect to the central telephone number is able to participate in the call. It is further noted that dial-in conference facilities also have limits on the number of simultaneous callers.
However, the mobile radio system has a number of advantages over the conference call. The multi-party session does not have to be arranged in advance. As long as the base station is operational, any mobile unit can connect. Upon doing so, the connecting unit will be connected to any of the mobile units which are currently switched on to the appropriate channel.
A service that offers a combination of the advantages of group radio and telephone conferencing is provided by telephone networks that use the Integrated Dispatch Enhanced Network (iDEN) system of cellular technologies. The iDEN solution is not applicable to the currently widespread cellular technologies, such as GSM, because it is restricted to iDEN supporting networks only. The iDEN solution cannot support devices on any other kind of network and certainly cannot support groups that encompass more than one network.
The iDEN service is thus unable to provide cross-network functionality, meaning that participation is limited to users of the iDEN service.